Tsunami (soo-NAH-mee) is a Japanese word meaning harbor wave. Tsunamis are caused by underwater earthquakes. Shockwaves cause the water level to rise above sea level, then gravity pulls the water into a giant wave. They can travel at speeds of 805 km/h (as fast as a jet plane).

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Tsunamis are NOT tidal waves. Tidal waves are caused by the forces of the moon, sun, and planets upon the tides, as well as the wind as it moves over the water. With typical waves, water flows in circles, but with a tsunami, water flows straight. This is why tsunamis cause so much damage!

 

Tsunamis are generally unnoticed out in the ocean, forming only a slight swell. As the tsunami approaches the shore and hits shallow water, it slows down but increases in height. A typical wave period for a destructive tsunami is about 12 minutes. During this time, the wave will both peak and recede, causing wide-spread destruction on land and sweeping debris back out to sea.

 

The Pacific Tsunami Warning System, based in Hawaii, monitors seismic activity in the Pacific Ocean. When large underwater earthquakes are detected, tsunami warnings can be issued to affected populations.

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On the average, two tsunamis occur per year throughout the world which inflict damage near the source. Approximately every 15 years a destructive, ocean-wide tsunami occurs.